The present invention relates to the processing of black liquor and the preparation of bitumen compositions containing black liquor.
Black liquor is an aqueous alkaline pulping residue produced in Kraft pulping of wood chips in a pulp mill to provide wood fibers for paper-making. Black liquor generally contains about 55 to 65% solids comprising lignin, sodium salts of poly-saccharinic acids, organic and inorganic sulfides and carbonates and many other compounds. The lignin in the black liquor is the main organic component and is present as a high mass colloid stabilized by ionized phenolic groups. Lignin is a phenylpropane polymer of amorphous structure comprising about 17 to about 30% of wood. Lignin is so closely associated with the cellulosic fibres and hemi-cellulose that makes up the balance of woody material that lignin can be separated from wood only by chemical reaction at high temperature, such as that used in the Kraft pulping process, wherein wood chips are digested with an aqueous alkaline solution of sodium hydroxide and hydrogen sulfide, known as white liquor. Normally, the black liquor, after separation of the wood fibers, is processed to remove organic materials and to recover and regenerate pulping chemicals. Lignin can be recovered from wood-processing wastes only in limited quantities.
The lignin is a natural binder derivative of wood. Alkali lignin from both softwoods and hardwoods are useful in many products. They are used as stabilizers for asphalt emulsions, modifiers and extenders for latex emulsions, compounding agents in vinyl plastics, soil conditioners, binders in printing inks, wood stains, protective colloids in soap emulsions, dispersing agents for clay, fire foam stabilizers, drilling mud additives, insecticide dispersants, absorbers in storage batteries and foundry sand binders. Alkali lignin can also be used as adhesives for plywood, molding powers and formed insulating resins and as a reinforcing agent for rubber.
Asphalt binders (or bitumen) are widely used in different applications, such as asphalt-aggregate blends for road paving, asphalt fiber reinforced membranes for roofing and asphalt-water emulsions in surface treating both for paving and roofing. Problems for straight-run asphalt in those applications are the tendency to become brittle at low temperatures and to become soft at high temperatures, the tendency to flow under constant load at service temperatures and the tendency to phase separation during storage when mixed with other components.
Various approaches have been used for the purpose of improving asphalt compositions to address these problems. For instance, polymers have been utilized to improve the high and low temperature characteristics of asphalt compositions, as well as to improve their toughness and durability. Air blowing of straight-run asphalt has been used to improve stiffness and dimensional stability for hot applied roofing systems. The asphalt may be treated with acid to improve its compatibility with the polymeric additives. Lignin or lignin based additives have been widely used to emulsify asphalt to achieve a stable dispersion of asphalt in aqueous medium.
Black liquor is an aqueous colloidal system in which ample lignin is present. However, means have not been previously disclosed whereby a stable dispersion of lignin in asphalt can be achieved by combining black liquor with hot liquid asphalt. When the black liquor is added to the bitumen and dispersed with agitation into molten asphalt cement, de-watering of the black liquor occurs while lignin and other salts in the black liquor tend to form large, rigid aggregates which separate from the liquid asphalt and subsequently strongly resist dispersion in the asphalt.
It is the objective of the present invention to develop a process or processes whereby liquor-solid pulping residue (black liquor) can be converted from one in which water is the dispersing and plasticizing agent to one in which water is replaced by oil, achieving a dispersion in which a lignin based colloidal particulate phase is stably maintained. It is another objective to provide a lignin-oil dispersion which can be smoothly blended with liquid asphalt to produce a stable, homogeneous dispersion.
The present invention relates to compositions and methods for combining black liquor with selected petroleum-derived products. More specifically, this invention provides two separate processes for preparing lignin-based colloidal dispersions in lubricating or other petroleum-based oils. The lignin-oil colloidal dispersions prepared by either of such processes may be blended with bitumen to produce novel bituminous composition. Two embodiments of such procedures are described herein. The black liquor used in the invention may be that resulting from cooking wood in an alkaline solution in the soda or sulfate (Kraft) paper-making process.
The asphalt employed in this invention can be any of the well known bituminous substances derived from petroleum, shale oil, coal tar and the like. Commonly, the asphalt is prepared by vacuum distillation of a topped crude oil. Preferably, the asphalt has a penetration at 25xc2x0 C. (as determined by ASTM D5) ranging for about 20 to about 400.
In a first embodiment of the invention, the procedure involves essentially two steps. In the first step, the black liquor is converted from its aqueous colloidal system to an anhydrous colloidal dispersion in a lubricating oil medium in which a surfactant, which may be an anionic surfactant, such as DDBSA (dodecylbenzene sulfuric acid), is used to promote the provision of the anhydrous colloidal dispersion. The process may be effected under low shear conditions.
The anhydrous colloidal dispersion of lignin in oil may be mixed, in a second step, with asphalt bitumen, producing a unique combination, which is a novel bituminous composition.
In another embodiment of the invention, the procedure again involves essentially two steps. First, bitumen is treated with an inorganic acid, such as sulfuric acid, at elevated temperature to provide an acid-treated bitumen. The black alkaline liquor is then added slowly to the acid-treated bitumen under agitation for de-watering the black liquor at a controlled rate to form a stable, substantially anhydrous, colloidal dispersion of lignin in the bitumen, also to provide a novel bituminous composition.
Accordingly, in another aspect of the present invention, there is provided a bituminous composition comprising bitumen, and dewatered lignin-containing spent alkaline pulping liquor dispersed therein. The dewatered spent alkaline pulping liquor may be present in an amount up to about 50 wt. % of the bitumen, preferably about 5 to about 25 wt. % of the bitumen.
In such composition, the dewatered spent alkaline pulping liquor may comprise an anhydrous colloidal dispersion of lignin in a lubricating oil. The dewatered spent alkaline pulping liquor may comprise a stable, substantially anhydrous, colloidal dispersion of lignin in the bitumen.
Referring first to the first embodiment of the invention, a lubricating oil is mixed with black liquor at temperatures below the water boiling point. A surfactant, which may be DDBSA (dodecylbenzene sulfuric acid), is selected to be added to the mixture to facilitate the colloidal dispersion of black liquor in the lubricating oil while de-watering is gradually carried out at an elevated temperature. The dewatering may be effected by starting at an elevated temperature, which may be about 100xc2x0 to about 180xc2x0 C., preferably about 110xc2x0 to about 160xc2x0 C. The resulting cream-like paste product is miscible with hot liquid asphalt at any ratio to form a novel bituminous composition.
The lubricating oil used in the first embodiment of the invention may be a re-refined waste motor oil or other convenient petroleum-based oil. Contaminants of waste motor oil, such as dirt, lead, arsenic and other harmful metals and chemicals, are removed from the waste motor oil to produce a clean base lubricating oil by the re-refining process.
The lubricating oil may be a selected fraction of refined mineral oil used for lubrication of moving surfaces. Such fraction may range in consistency from thin liquid to grease-like substances. Usually, lubricating oils contain small amounts of additives to impart special properties, such as viscosity index and detergency.
The surfactant or dispersing agent used in the process may typically be dodecylbenzene sulfuric acid (DDBSA), although other anionic surfactants may be employed, if desired, such as fatty acid, linear alkyl sulfonates having 10 or more carbon atoms in the chain. DDBSA is benzene with dodecene, and the resulting dodecylbenzene is sulfonated. DDBSA may be neutralized with caustic soda from the alkaline black liquor or other convenient source to promote the detergency of the lubricating oil and to reduce surface tension in the mixture.
However, a surfactant need not always be necessary, if the lubricating oil employed has a detergency high enough to ensure that a colloidal dispersion of the solid residue from the black liquor is achieved in the lubricating oil medium.
The lignin-oil dispersion produced by either of these procedures may be smoothly blended with bitumen to provide the desired lignin-asphalt composition. The spent pulping liquor, which may be black liquor from a kraft pulp mill, may be present in an amount of about 25 to about 60 wt. % of the composition, preferably about 25 to 40 wt. % of the composition.
Referring now to the second embodiment of the invention, the bitumen first is treated with a strong mineral acid, such as sulfuric acid, at elevated temperature and then the alkaline black liquor is added to the treated bitumen at a controlled rate under agitation to effect de-watering of the black liquor to form a stable, substantially anhydrous, colloidal dispersion in the bitumen. The elevated temperature may be about 100xc2x0 to about 180xc2x0 C., preferably about 110xc2x0 to about 160xc2x0 C. The spent pulping liquor may be present in an amount of about 5 to about 50 wt. % of the composition, preferably about 10 to about 30 wt. %
An inorganic acid is contacted with, or added to, the asphalt to form an acid treated asphalt. In general, the acid addition shifts the asphalt structure from a sol to a gel, lowers the temperature susceptibility of the asphalt and improves the stability of the additive dispersion in the treated asphalt. Since black liquor is an aqueous alkaline system, it is critical that the acid not be added to the asphalt after addition of or with the black liquor.
Preferably, the acid is added slowly to the asphalt to avoid foaming, which may occur if all the acid were added at one time. The inorganic acid content of the asphalt resulting from the acid treatment is not critical, but normally is in the range between about 0.2 and about 3.5 wt %, preferably between about 0.5 and about 2.5 wt % of the asphalt. Although a wide variety of inorganic acids can be used for treatment of the asphalt, the inorganic acid is preferably selected from the group consisting of sulfuric acid, phosphoric acid, poly-phosphoric acid, phosphorous pentoxide, hydrochloric acid, and mixtures thereof. The sulfuric acid, phosphoric acid or poly-phosphoric acid are preferred inorganic acids, with the sulfuric acid being particularly preferred.
Following acid addition, the alkaline black liquor is then added slowly to the acid-treated bitumen at an elevated temperature, typically around 100xc2x0 C., under agitation for a certain period of time to permit de-watering of the black liquor to occur while the solids are incorporated into the bitumen. The temperature of the final composition next is increased above the boiling point of water, typically up to around 160xc2x0 C. until residual water is completely evaporated off to form a stable, substantially anhydrous, colloidal lignin dispersion in the bitumen.